1. Field of the Invention
The present invention relates to an optical fiber cord having connectors, and also to an optical coupling set including such an optical fiber cord.
2. Description of the Background Art
Recently, optical fibers (holey fibers) having multiple holes along optical axes thereof have been developed. In a typical holey fiber, light is confined in the core region by means of difference in effective refractive index between the core region and the cladding region as generated by plurality of holes, or by means of a photonic band gap generated by a photonic crystal structure. In such a holey fiber, bending loss is smaller as compared to a conventional optical fiber and various dispersion characteristics can be obtained.
A technique of changing optical transmission characteristics by filling the holes of a holey fiber with Xenon (Xe) gas has been disclosed by Dimitre G. Ouzounov (eight others) in “Generation of Megawatt Optical Solutions in Hollow-Core Photonic Band-Gap Fibers”, Science, Sep. 19, 2003, Vol. 301, pp. 1702–1704.
Holey fibers are disadvantageous in that loss increases if there are impurities in the holes. Accordingly, a method of preventing impurities from entering the holes by fusing both ends of the fiber and sealing the openings of the holes in the manufacturing process of the fiber has been proposed. However, in this method, ambient gas or the atmosphere in which the fiber material is drawn will be trapped in the holes, which results in increase of absorption loss of light in 2.76-μm and 1.38-μm bands, the light being absorbed by water vapor, or increase of absorption loss of vacuum ultraviolet light which is absorbed by oxygen molecules. Therefore, the holes are preferably evacuated to vacuum or filled with a gas that does not absorb light to be guided. In addition, since holey fibers are attached to various optical apparatuses, the ends thereof are preferably configured to be detachable. Although Dimitre G. Ouzounov et. al. suggest filling the holes with Xe gas, neither a method for filling the holes nor a structure for encapsulating the Xe gas is described.